1. Field of Invention
This invention relates to thermally-responsive record material. It more particularly relates to such record material in the form of sheets coated with color-forming systems comprising chromogenic material, and acidic color developer. This invention particularly concerns a thermally-responsive record material capable of forming an image resistant to fade or erasure. The invention teaches a record material having improved image density retention.
2. Description of Related Art
Thermally-responsive record material systems are well known in the art and are described in many patents, for example, U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318; and 4,470,057 which are incorporated herein by reference. In these systems, basic chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark.
Thermally-responsive record materials have characteristic thermal responses, desirably producing a colored image of sufficient intensity upon selective thermal exposure.
A drawback of thermally-responsive record materials limiting utilization in certain environments and applications has been the undesirable tendency of thermally-responsive record materials upon forming an image to not retain that image in its original integrity over time when the thermally-responsive record material is handled or exposed to common liquids or oils or plasticizers such as found in skin oil, plastic food wrap, cooking oil and common carbonless paper solvents. As a result, a high degree of care and control in handling imaged thermally-responsive record materials has been required. This loss of image density and fade can be not only annoying but potentially damaging commercially whenever the integrity of records is allowed to become suspect through improper record storage.
To impart ability to a thermally-responsive record material to resist image fading or erasure upon contact with common oils, solvents or plasticizers would be an advance in the art and of commercial significance.
It is an object of the present invention to disclose a thermally-responsive record material having improved image retention and resistance to fade or erasure. The record material of the invention is remarkably resistant to fade or erasure from one or more common external challenges including contact with saponified fats or common oils, skin oil, internal phase (IP) solvents (carbonless solvents), plasticizers, or high heat and humidity such as in a 90.degree. F./90% humidity test chamber.
It is an object of the present invention to disclose a thermally-responsive record material comprising a support member bearing a thermally-sensitive color forming composition comprising chromogenic material and acidic developer material in substantially contiguous relationship, whereby the melting, softening or sublimation of either material produces a change in color by reaction between the two, an ascorbic acid ester, optionally but preferably a modifier and a suitable binder therefor.